1. Field of the Invention
The invention relates in general to a controller used to control multiple motors, each associated with an axis of movement, wherein the controller is a modular controller, and a method of operating such a multiple axis modular controller.
2. Description of the Related Art
In conventional controllers for a system including multiple subsystems, such as a wafer inspection system, each subsystem is provided with a control unit. For a large system controlling motors along multiple axes of movement, not only must the control units for each subsystem communicate with the motors to which they are connected, they must be able to communicate with each other. For example, in a wafer inspection system, a robot that is transferring a wafer to an inspection stage must know when the stage has secured the wafer so that the robot can stop its motion and release its hold on the wafer.
Conventionally, the position, movement, power level, and other parameters for control of each subsystem of a system are coordinated by a central control unit. The individual pieces of information required by each actuator, such as a servo motor of a robot, are conveyed through the control unit to the central controller, which sends actuating signals to the individual actuators through the appropriate control unit of a subsystem. This can result in a substantial processor burden on the central controller, resulting in slow operation of the system controlled. Further, the more complex the system controlled, the more complex the electrical connections due to the extensive wiring and cabling to the central controller.
Efforts to speed up these operations using faster processor in control units have been made, but they fail to address the resulting complex electrical connections. Also, the complexity of desired operation of systems controlled by these controls units progresses at pace with the increased speeds, with the result that processing delays are still experienced. The combination of speed and processing delays can cause errors in the operation of the system. Increased complexity also increases the risk that the failure of an individual control unit will cause failure of the operation of the entire system, potentially damaging any product in the system.